In recent years extensive research has been devoted to the alleviation of air pollution in many metropolitan areas. Part of this effort has been directed to methods of reducing the hydrocarbon, carbon monoxide and nitrogen oxide content of the exhaust gas of internal combustion engines. Various catalytic converter systems have been proposed to accomplish this. With such systems, the exhaust gases are passed through a catalytic bed whereupon the noxious materials are converted to an inactive form.
Manganese-containing catalysts have been proposed for use in the above catalytic converters. In U.S. Pat. No. 3,207,704, an alumina supported manganese catalyst is disclosed which may optionally be promoted with lead, copper, chromium, barium, titanium, cerium or tin. In U.S. Pat. No. 3,024,593, a list of ten suitable catalytic metals is disclosed which includes individually manganese and palladium. The only mixture actually disclosed is copper-chromium. U.S. Pat. No. 2,071,119 has a similar disclosure and contains a list of catalytically active metals which includes manganese and palladium, but does not disclose the combination of manganese and palladium. West German Pat. No. 1,442,743 discloses alumina catalysts treated with solutions of manganese, palladium and/or silver, optionally with nickel and/or cobalt and/or iron. In West German Pat. No. 1,268,907, a catalyst is disclosed containing copper oxide, manganese oxide, chromia and palladium on an alumina, silica-alumina or clay support.
Certain of the catalysts described herein are on a support which is precoated with a rare earth metal oxide. Catalysts containing rare earth metal oxides are disclosed in U.S. Pat. Nos. 3,291,564; 3,483,138; 3,545,917; 3,226,340; 3,453,333; 3,395,004; 3,284,370; 3,153,635; 2,945,057; 2,152,908; 2,148,129; 2,129,733, and British Pat. No. 1,231,276.